1. Field of the Invention
The present invention relates to an electrophotographic photoconductor comprising an electroconductive substrate, and a photoconductive layer which comprises a charge generation layer and a charge transport layer successively formed on the substrate in this order.
2. Discussion of Background
Recently, organic photoconductors (OPC) are widely used in copying machines and printers. Such organic photoconductors comprise, for example, a substrate and a photoconductive layer. The photoconductive layer may comprise a charge generation layer (CGL) and a charge transport layer (CTL) which are successively overlaid on the substrate. The CTL is in the form of a film which comprises a low-molecular-weight charge transporting material which is dispersed in a binder resin in a certain concentration. The addition of the charge transporting material to the binder resin causes deterioration of the mechanical strength of the binder resin itself, and therefore, the CTL is fragile and has a low tensile strength. It is considered that the above-mentioned deterioration of the mechanical strength of the binder resin in the CTL causes some problems of the photoconductor, such as wear, flaw, peeling, and crack.
It is proposed to employ a high-molecular-weight material as the charge transporting material in the CTL. For instance, polymers such as polyvinylcarbazole, polyvinyl anthracene and polyvinyl pyrene reported by M. Stolka in J. POLYM. SCI. VOL. 21, 969; and a vinyl polymer of hydrazone described in '89 JAPAN HARD COPY p. 67 are proposed to use as charge transporting materials in the CTL. However, a film of the CTL is still fragile and sufficient mechanical strength cannot be obtained. In addition, the above-mentioned high-molecular-weight materials have shortcomings in the sensitivity and the mobility of hole in practice, which induces high residual potential and decreases the durability of a photoconductor.
To solve the aforementioned problems of the CTL, there is proposed a method for forming the CTL by previously dispersing a charge transporting material in a binder resin and then curing the binder resin. In this proposal, however, the content of the charge transporting material is as high as 30 to 50 wt. % in the CTL, so that a sufficient curing reaction is not carried out and the charge transporting material easily falls off from the binder resin. The problem of the wear of the photoconductor has not yet solved.